Pausing only to train gun barrels around corners or scan rooftops for insurgents, they bound across desolate roads lined with broken glass and charred cars — and start running again.

Standing still is rarely an option in this insurgent-plagued metropolis beset by roadside bombs, rocket fire and, Marines here say, the worst sniper threat on the planet.

“Every time we go out, we run,” said 2nd Lt. Brian Wilson, a 24-year-old platoon commander from Columbia, S.C. “If you stand still, you WILL get shot at.”

And most of the time, Marines shoot back.

Buildings around Government Center, the Marine-defended headquarters of provincial government, offer stark evidence of fighting between insurgents and U.S. forces in downtown Ramadi, a city 70 miles west of Baghdad in the heart of the Sunni Arab-dominated insurgency.

Some buildings have been blown away by air strikes, their walls ripped open, their twisted floors collapsed. Others, including a small mosque and its tank-blasted minaret, are riddled with rocket and bullet impacts. Plastic awnings over shop fronts are shredded. Power lines hang down along sidewalks.

Marines patrolling this city on foot don’t like to stay exposed too long, preferring instead to blow front gate locks off private homes with special shotgun shells to take temporary cover in walled courtyards before moving on. They don’t knock first — there is no time.

On one recent sweep, U.S. and Iraqi infantrymen climbed over walls between houses instead of risking the streets outside.

“We try to stay mobile so snipers can’t aim in on us,” said 1st Lt. Carlos Goetz, a 29-year-old Miami native. “If we walk, then it gives them more time to aim in on your head.”

Running around with 60 to 80 pounds of gear, the Marines’ pace is more of a quick jog.

“You try to take cover wherever you can, but it just feels like someone’s always watching you. It really messes with your head,” said Cpl. Jason Hunt of Wellsville, N.Y.

“You look for dark windows, tiny holes anywhere,” the 24-year-old said. “They could be sitting back on a bench with a scope and a barrel — they see you, but you can’t see them.”

Troops from the 3rd Battalion, 8th Marine Regiment aggressively patrol the blown-out district around Government Center at all hours — conducting raids and sweeps during the hazy, gritty heat of the day, and in the quiet of night when moonlight casts buildings and villas in blue hues.

Marines say the patrols have disrupted insurgent operations. But the guerrillas operating in small teams are relentless, firing rockets, mortars and machine guns daily at Government Center, U.S. bases and fortified observation posts. Sometimes they attack the same targets several times a day.

Goetz said Marines patrol hoping to bring insurgents out into the open, where they are little match for the overwhelming U.S. firepower.

It usually doesn’t take long.

“It takes about eight minutes from us stepping outside of the wire and getting across the street to the time that we start receiving contact from the enemy,” Goetz said at Goverment Center.

The safety-in-motion logic also applies to U.S. vehicles. Drivers roll back and forth in danger zones, rather than park, to make their vehicles harder targets, particularly for rocket-propelled grenades, or RPGs.

One young Marine manning a machine gun in a Humvee turret outside Government Center was hit by an RPG and killed instantly just before the vehicle rolled inside. In recent weeks, another Marine was killed by a sniper’s bullet that tore through his shoulder toward his heart.

Two Iraqi soldiers were fatally shot manning a guard post — one as he walked out of it and one who went to save him, said Marine Capt. Carlos Barela, 35, of Albuquerque, N.M.

Out on the streets, troops are wary of all the spots that insurgents have used to hide bombs: heaps of garbage and rubble, mangles of wires, scrap metal, the occasional dead animal or body part.

“This is the kind of stuff that makes you cringe,” said Capt. Andrew Del Gaudio, 30, of Mount Laurel, N.J., gesturing at a large pile of dirt near a light pole as he ran along ahead of a raid with a platoon from his Kilo Company.

Sprinting into the entrance of an abandoned building on another day and seeing a bag on the ground with wires sticking out, Marines quickly retreated as one shouted, “Get out! Go! Go! Go!”

One Iraqi soldier bounding between two roads this month stepped on a bomb that blew off his leg. It’s easier to spot bombs when moving slowly, but speed is the rule for Marines in Ramadi.

Cpl. Scott R. Gibson, 22, of Carlisle, Pa., said his platoon had started off walking during their first patrol in the city last month, worrying about pressure-plate bombs that explode when stepped on.